Image coding method, image decoding method, image coding apparatus, image decoding apparatus, and image coding and decoding apparatus

ABSTRACT

An image coding method includes: writing, into a sequence parameter set, buffer description defining information for defining a plurality of buffer descriptions; selecting one of the buffer descriptions for each processing unit that is a picture or a slice, and writing buffer description selecting information for specifying the selected buffer description, into a first header of the processing unit which is included in the coded bitstream; and coding the processing unit using the selected buffer description, and the buffer description defining information includes long-term information for identifying, among a plurality of reference pictures indicated in the buffer descriptions, a reference picture to be assigned as a long-term reference picture.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/531,760 filed on Sep. 7, 2011. The entire disclosureof the above-identified application, including the specification,drawings and claims is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to image coding methods, image decodingmethods, image coding apparatuses, image decoding apparatuses, and imagecoding and decoding apparatuses, and particularly to an image codingmethod and an image decoding method each of which uses a bufferdescription for specifying a picture to be held in a buffer.

BACKGROUND

State-of-the-art video coding schemes, such as MPEG-4 AVC/H.264 (see NonPatent Literature 1) and the upcoming HEVC (High-Efficiency VideoCoding), perform coding of image or video content using inter-pictureprediction from previously coded or decoded reference pictures. In otherwords, the video coding schemes exploit the information redundancyacross consecutive pictures in time. In MPEG-4 AVC video coding scheme,reference pictures in the decoded picture buffer (DPB) are managedeither using a predefined sliding-window scheme for removing earlierpictures in coding order from the DPB, or explicitly using a number ofbuffer management signals in the coded bitstream to manage and removeunused reference pictures.

CITATION LIST Non Patent Literature

-   [Non Patent Literature 1] ISO/IEC 14496-10 “MPEG-4 Part10 Advanced    Video Coding”

SUMMARY Technical Problem

In the image coding method and the image decoding method which adoptsuch video coding schemes, there are demands for a further improvementin coding efficiency.

Thus, one non-limiting and exemplary embodiment provides an image codingmethod or an image decoding method in which the coding efficiency canimprove.

Solution to Problem

An image coding method according to an aspect of the present disclosureis an image coding method for generating a coded bitstream by coding animage using a buffer description for specifying a picture to be held ina buffer, the image coding method comprising: writing, into a sequenceparameter set, buffer description defining information for defining aplurality of buffer descriptions; selecting one of the bufferdescriptions for each processing unit that is a picture or a slice, andwriting, into a first header of the processing unit, buffer descriptionselecting information for specifying the selected buffer description,the first header being included in the coded bitstream; and coding theprocessing unit using the selected buffer description, wherein thebuffer description defining information includes long-term informationfor identifying, among a plurality of reference pictures indicated inthe buffer descriptions, a reference picture to be assigned as along-term reference picture.

These general and specific aspects may be implemented using a system, amethod, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Additional benefits and advantages of the disclosed embodiments will beapparent from the Specification and Drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

The present disclosure provides an image coding method or an imagedecoding method in which the coding efficiency can improve.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 shows an example of a picture referencing structure.

FIG. 2 shows a structure of a coded bitstream.

FIG. 3 is a block diagram of an image coding apparatus according toEmbodiment 1 of the present disclosure.

FIG. 4 is a flowchart of an image coding method according to Embodiment1 of the present disclosure.

FIG. 5 shows a structure of a coded bitstream according to Embodiment 1of the present disclosure.

FIG. 6 shows a structure of a coded bitstream according to a variationof Embodiment 1 of the present disclosure.

FIG. 7 is a block diagram of an image decoding apparatus according toEmbodiment 1 of the present disclosure.

FIG. 8 is a flowchart of an image decoding method according toEmbodiment 1 of the present disclosure.

FIG. 9 is a flowchart of an image coding method according to Embodiment2 of the present disclosure.

FIG. 10 shows a structure of a coded bitstream according to Embodiment 2of the present disclosure.

FIG. 11 shows a structure of a coded bitstream according to a variationof Embodiment 2 of the present disclosure.

FIG. 12 is a flowchart of an image decoding method according toEmbodiment 2 of the present disclosure.

FIG. 13 is a flowchart of an image coding method according to Embodiment3 of the present disclosure.

FIG. 14 shows a structure of a coded bitstream according to Embodiment 3of the present disclosure.

FIG. 15 shows a structure of a coded bitstream according to a variationof Embodiment 3 of the present disclosure.

FIG. 16 is a flowchart of an image decoding method according toEmbodiment 3 of the present disclosure.

FIG. 17 is a flowchart of an image coding method according to Embodiment4 of the present disclosure.

FIG. 18 shows a structure of a coded bitstream according to Embodiment 4of the present disclosure.

FIG. 19 shows a syntax structure of a sequence parameter set accordingto Embodiment 4 of the present disclosure.

FIG. 20 shows a syntax structure of a slice header according toEmbodiment 4 of the present disclosure.

FIG. 21 is a flowchart of an image decoding method according toEmbodiment 4 of the present disclosure.

FIG. 22 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 23 shows an overall configuration of a digital broadcasting system.

FIG. 24 shows a block diagram illustrating an example of a configurationof a television.

FIG. 25 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 26 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 27A shows an example of a cellular phone.

FIG. 27B is a block diagram showing an example of a configuration of acellular phone.

FIG. 28 illustrates a structure of multiplexed data.

FIG. 29 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 30 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 31 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 32 shows a data structure of a PMT.

FIG. 33 shows an internal structure of multiplexed data information.

FIG. 34 shows an internal structure of stream attribute information.

FIG. 35 shows steps for identifying video data.

FIG. 36 is a block diagram showing an example of a configuration of anintegrated circuit for implementing the moving picture coding method andthe moving picture decoding method according to each of embodiments.

FIG. 37 shows a configuration for switching between driving frequencies.

FIG. 38 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 39 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 40A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 40B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DESCRIPTION OF EMBODIMENTS Underlying Knowledge Forming Basis of thePresent Disclosure

Recent developments in the HEVC video coding scheme include theintroduction of DPB management using buffer descriptions. The bufferdescriptions are also called a reference picture set. The bufferdescription defines the pictures that are retained in the DPB, insteadof defining the pictures that are to be removed from the DPB. In otherwords, the buffer description is a list of picture identifiersindicating all reference pictures stored in the DPB. Furthermore, thebuffer description is an absolute description of a plurality ofreference pictures stored in a buffer which are to be used in a processof decoding the coded pictures to be processed currently or in thefuture. Each item in this list is referred to as a buffer element. Abuffer element contains a picture identifier unique to each picture,such as a picture order count (POC) number, and additional informationof the picture such as a temporal_id value.

This buffer description is activated at the start of coding or decodingof a picture. Pictures that are not included in the active bufferdescription are removed from the DPB. Benefits of this bufferdescription include improved robustness against transmission/deliverylosses and simplified handling of non-existent pictures.

In some cases, multiple pictures in a video sequence share the samepicture referencing structure. For example, a low delay coding structureuses a periodic clustering structure in which the same layer structureis periodically repeated in unit of four pictures as shown in FIG. 1.This repeating unit (that is four pictures herein) is called a cluster.

In the example shown in FIG. 1, the picture numbers (P0 to P12) indicateboth unique coding order and unique display or output order of pictures.The pictures P0, P4, P8 and P12 constitute the first layer of pictures.These pictures are coded with the highest quality, for example, byapplying quantization least strongly. Pictures P2, P6 and P10 constitutethe second layer. These pictures are coded with lower quality than thefirst layer. Pictures P1, P3, P5, P7, P9 and P11 constitute the thirdlayer. These pictures are coded with the lowest quality. In such aperiodic referencing structure, pictures located at the same relativeposition within their clusters (for example P1, P5 and P9) usually usethe same relative picture referencing structure. For example, thepicture P5 uses the pictures P4 and P2 as reference pictures, while thepicture P9 uses the pictures P8 and P6 as reference pictures.

In order to accommodate periodic clustering structures such as the abovestructure, a conceivable approach is periodic signaling of bufferdescriptions. This buffer description specifies the temporal distancesor positions of the reference pictures relative to a target picture tobe coded or decoded. By so doing, the reference pictures stored in theDPB can be specified. For example, this buffer description is signalledonce in the picture parameter set (PPS). This buffer description is thenreferred to repeatedly in the slice headers of the pictures having thesame relative position within a cluster. For example, a bufferdescription specifying relative positions of {−1, −3} can be used inboth P5 to specify {P4, P2} as reference pictures and by P9 to specify{P8, P6} as reference pictures.

FIG. 2 shows an example of the signaling structure of buffer descriptionin this case. A coded bitstream 500 shown in FIG. 2 includes a sequenceparameter set (SPS) 501 (SPS0), a plurality of picture parameter sets(PPSs) 502 (PPS0 and PPS1), and a plurality of picture data 503. Each ofthe picture data 503 includes a plurality of slice data 535. Each of theslice data 535 includes a slice header 541 and a slice data part 542.The slice data part 542 includes a plurality of coding unit (CU) data543.

Each of the PPSs 502 includes a PPS identifier 522 (pps_id) and bufferdescription defining information 512 (BD define). The buffer descriptiondefining information 512 indicates a plurality of buffer descriptions515 (BD0 to BDn). Each of the buffer descriptions 515 includes aplurality of buffer elements 515A (BE0 to BE2).

Thus, the plurality of buffer descriptions 515 are defined using thebuffer description defining information 512 in the picture parametersets 502. Each of the PPSs 502 is identified by a PPS identifier 522unique to the PPS.

The slice header 541 includes PPS selecting information 533 (pps_select)and buffer description updating information 523 (BD update).

The PPS selecting information 533 indicates the PPS 502 referred toduring coding or decoding of the slice. In the example in FIG. 2,pps_select=0 is satisfied, and the PPS0 having pps_id=0 is selected.

The buffer description updating information 523 includes informationwhich specifies the buffer description selected out of the bufferdescriptions 515. In the example in FIG. 2, the buffer description BD1is selected. Additionally, the buffer description updating information523 includes buffer description modifying information. The bufferdescription modifying information assigns a picture identifier to aselected buffer element 515A within the selected buffer description 515.Here, the picture identifier is specified either using its relativeposition or using an identifier unique to the picture. The identifierunique to the picture includes, for example, the picture order count(POC) number. In the example in FIG. 2, the picture P₂₁₄ identified byits POC number=214 is assigned to the buffer element BE0 within thebuffer description BD1. This modification applies only to the currenttarget slice and does not apply to subsequent slices. When themodification of the same content (e.g. assigning the picture P₂₁₄ to thebuffer element BE0) is required in subsequent slices or pictures thatuse the buffer description BD1, the slice headers of those subsequentslices or pictures shall include the buffer description updatinginformation 523 of the same content.

Recent video coding schemes support the use of long-term referencepictures, which are reference pictures that remain in the DPB for arelatively long period of time and are used as inter-predictionreference pictures for coding a plurality of pictures during thisperiod. In AVC video coding scheme, long-term reference pictures in theDPB are managed using the memory management control operation (MMCO)process.

In the above buffer description, long-term reference pictures aredefined and managed in the following manner. A reference picture isregarded as a long-term reference picture when the picture is assignedto a buffer element by specifying its POC number. On the other hand, apicture is regarded as a non-long-term (short-term) reference picturewhen the picture is assigned to a buffer element by specifying therelative distance (POC distance) to a target picture. A long-termreference picture remains in the DPB as long as every consecutive bufferdescription includes it.

The parameters for specifying a long-term reference picture areavailable only at the slice header. Therefore, in order to keep along-term reference picture in the DPB over a range of consecutivepictures, every slice header within the range of consecutive picturesshall contain the buffer description updating information 523 whichidentifies the long-term reference picture.

Thus, in the above technique, the information for assigning a long-termreference picture applies only to the slice to be coded or decoded. Inaddition, in order to use the long-term reference picture for a longperiod of time, the coded bitstream shall include plural pieces ofinformation which indicate the same assignment.

Thus, the inventors found the first problem of a decrease in codingefficiency which is due to repeated information included in the codedbitstream.

Furthermore, in the above technique, a unique picture number (POCnumber) is used as information identifying the long-term referencepicture. This POC number may have a large value and therefore requiresmany bits. In practice, few long-term reference pictures are used at onetime. Hence, it is not necessary to use a large value for identifyingeach long-term reference picture.

Thus, the inventors found the second problem of a decrease in codingefficiency which is due to many bits being necessary to specify along-term reference picture.

In order to solve the aforementioned problems, an image coding methodaccording to an aspect of the present disclosure is an image codingmethod for generating a coded bitstream by coding an image using abuffer description for specifying a picture to be held in a buffer, theimage coding method comprising: writing, into a sequence parameter set,buffer description defining information for defining a plurality ofbuffer descriptions; selecting one of the buffer descriptions for eachprocessing unit that is a picture or a slice, and writing, into a firstheader of the processing unit, buffer description selecting informationfor specifying the selected buffer description, the first header beingincluded in the coded bitstream; and coding the processing unit usingthe selected buffer description, wherein the buffer description defininginformation includes long-term information for identifying, among aplurality of reference pictures indicated in the buffer descriptions, areference picture to be assigned as a long-term reference picture.

By so doing, in the image coding method according to an aspect of thepresent disclosure, the buffer description defining informationincluding the long-term information for assigning a reference picture asa long-term reference picture is written into the sequence parameter setshared by a plurality of pictures, and the buffer description identifierindicating a buffer description to be selected is written into a headerof each picture or slice. This allows a reduction in redundantinformation and thereby allows an improvement in coding efficiency inthe image coding method as compared to the case where the informationfor assigning a reference picture as a long-term reference picture iswritten into a slice header.

For example, the long-term information may include a first long-termindex for identifying the reference picture to be assigned as thelong-term reference picture.

For example, the long-term information may further include a uniquepicture order count (POC) number for specifying a reference pictureassociated with the first long-term index.

For example, the first header may further include a second long-termindex for identifying the reference picture to be assigned as thelong-term reference picture.

Furthermore, an image decoding method according to an aspect of thepresent disclosure is an image decoding method for decoding a codedbitstream using a buffer description for specifying a picture to be heldin a buffer, the image decoding method comprising: obtaining, from asequence parameter set corresponding to the coded bitstream, bufferdescription defining information for defining a plurality of bufferdescriptions; obtaining, from a first header of a processing unit thatis a picture or a slice, buffer description selecting information forspecifying one of the buffer descriptions, the first header beingincluded in the coded bitstream; and decoding the processing unit usingthe buffer description specified in the buffer description selectinginformation, wherein the buffer description defining informationincludes long-term information for identifying, among a plurality ofreference pictures indicated in the buffer descriptions, a referencepicture to be assigned as a long-term reference picture.

By so doing, a bitstream coded with improved coding efficiency can bedecoded in the image decoding method according to an aspect of thepresent disclosure.

For example, the long-term information may include a first long-termindex for identifying the reference picture to be assigned as thelong-term reference picture.

For example, the long-term information may further include a uniquepicture order count (POC) number for specifying a reference pictureassociated with the first long-term index.

For example, the first header may further include a second long-termindex for identifying the reference picture to be assigned as thelong-term reference picture.

Furthermore, an image coding apparatus according to an aspect of thepresent disclosure is an image coding apparatus for generating a codedbitstream by coding an image using a buffer description for specifying apicture to be held in a buffer, the image coding apparatus comprisingwriting, into a sequence parameter set, buffer description defininginformation for defining a plurality of buffer descriptions; andselecting one of the buffer descriptions for each processing unit thatis a picture or a slice, and writing, into a first header of theprocessing unit, buffer description selecting information for specifyingthe selected buffer description, the first header being included in thecoded bitstream, wherein the buffer description defining informationincludes long-term information for identifying, among a plurality ofreference pictures indicated in the buffer descriptions, a referencepicture to be assigned as a long-term reference picture, and the imagecoding apparatus codes the processing unit using the selected bufferdescription.

By so doing, in the image coding apparatus according to an aspect of thepresent disclosure, the buffer description defining informationincluding the long-term information for assigning a reference picture asa long-term reference picture is written into the sequence parameter setshared by a plurality of pictures, and the buffer description identifierindicating a buffer description to be selected is written into a headerof each picture or slice. This allows a reduction in redundantinformation and thereby allows an improvement in coding efficiency inthe image coding apparatus as compared to the case where the informationfor assigning a reference picture as a long-term reference picture iswritten into a slice header.

Furthermore, an image decoding apparatus according to an aspect of thepresent disclosure is an image decoding apparatus for decoding a codedbitstream using a buffer description for specifying a picture to be heldin a buffer, the image decoding apparatus comprising a frame memorycontrol unit configured to perform the following: obtaining, from asequence parameter set corresponding to the coded bitstream, bufferdescription defining information for defining a plurality of bufferdescriptions; and obtaining, from a first header of a processing unitthat is a picture or a slice, buffer description selecting informationfor specifying one of the buffer descriptions, the first header beingincluded in the coded bitstream, wherein the buffer description defininginformation includes long-term information for identifying, among aplurality of reference pictures indicated in the buffer descriptions, areference picture to be assigned as a long-term reference picture, andthe image decoding apparatus decodes the coding unit using the bufferdescription specified in the buffer description selecting information.

By so doing, a bitstream coded with improved coding efficiency can bedecoded in the image decoding apparatus according to an aspect of thepresent disclosure.

Furthermore, an image coding and decoding apparatus according to anaspect of the present disclosure comprises the image coding apparatusand the image decoding apparatus.

These general and specific aspects may be implemented using a system, amethod, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Hereinafter, embodiments are described in greater detail with referenceto the Drawings.

Each of the embodiments described below shows a general or specificexample. The numerical values, shapes, materials, structural elements,the arrangement and connection of the structural elements, steps, theprocessing order of the steps etc. shown in the following embodimentsare mere examples, and therefore do not limit the present disclosure.Therefore, among the structural elements in the following embodiments,structural elements not recited in any one of the independent claimsdefining the most generic part of the inventive concept are described asarbitrary structural elements.

Four embodiments are described in the following. It will be apparent tothose skilled in the art that combinations of these embodiments can becarried out to further increase the usability and adaptability ofperiodic buffer description definitions.

Embodiment 1

In this embodiment, buffer description defining information includinglong-term information is written into the SPS. This allows a reductionin redundant information and thereby allows an improvement in codingefficiency as compared to the case where the long-term information iswritten into a slice header.

[Coding Apparatus]

FIG. 3 is a block diagram which shows a structure of an image codingapparatus 100 according to this embodiment.

The image coding apparatus 100 codes an input image signal 120 on ablock-by-block basis so as to generate a coded bitstream 132. As shownin FIG. 3, the image coding apparatus 100 includes a subtractor 101, anorthogonal transformation unit 102, a quantization unit 103, an inversequantization unit 104, an inverse orthogonal transformation unit 105, anadder 106, a block memory 107, a frame memory 108, an intra predictionunit 109, an inter prediction unit 110, a picture type determinationunit 111, a variable-length coding unit 112, and a frame memory controlunit 113.

The input image signal 120 is a video or image bitstream. The subtractor101 calculates a difference between prediction image data 131 and theinput image signal 120, thereby generating prediction error data 121.The orthogonal transformation unit 102 performs orthogonaltransformation on the prediction error data 121 to generate frequencycoefficients 122. The quantization unit 103 quantizes the frequencycoefficients 122, thereby generating quantized values 123. Thevariable-length coding unit 112 performs entropy coding (variable-lengthcoding) on the quantized values 123, thereby generating the codedbitstream 132.

The inverse quantization unit 104 inversely quantizes the quantizedvalues 123, thereby generating frequency coefficients 124. The inverseorthogonal transformation unit 105 performs inverse orthogonaltransformation on the frequency coefficients 122, thereby generatingprediction error data 125. The adder 106 adds the prediction error data125 and the prediction image data 131, thereby generating the decodedimage data 126. The block memory 107 holds the decoded image data 126 asdecoded image data 127 on a block-by-block basis. The frame memory 108holds the decoded image data 126 as decoded image data 128 on aframe-by-frame basis.

The intra prediction unit 109 performs intra prediction to generateprediction image data 129 of a current block to be coded. Specifically,the intra prediction unit 109 searches within the decoded image data 127stored in the block memory 107, and estimates an image area which ismost similar to the input image signal 120.

The inter prediction unit 110 performs inter prediction using theper-frame decoded image data 128 stored in the frame memory 108, togenerate prediction image data 130 of the current block.

The picture type determination unit 111 selects one of the predictionimage data 129 and the prediction image data 130 and outputs theselected data as the prediction image data 131.

The frame memory control unit 113 manages the decoded image data 128stored in the frame memory 108. Specifically, the frame memory controlunit 113 determines whether the decoded image data 128 is kept in theframe memory 208 or removed from the frame memory 208. Furthermore, theframe memory control unit 113 constructs reference lists to be used bythe inter prediction unit 110. Furthermore, the frame memory controlunit 113 generates frame memory control information 133 which includesthe buffer description defining information. The variable-length codingunit 112 generates the coded bitstream 132 which includes this framememory control information 133.

[Coding Process]

Next, a description is given to an image coding method which isperformed by the image coding apparatus 100 as mentioned above.

FIG. 4 is a flowchart of an image coding method according to thisembodiment. Furthermore, FIG. 4 shows a coding process which isperformed on a single video sequence including a plurality of pictures.

Firstly, the image coding apparatus 100 determines a plurality of bufferdescriptions which are to be used over a plurality of pictures in avideo sequence (S101). The buffer descriptions are used to specifypictures to be held in the buffer (frame memory). Specifically, each ofthe buffer descriptions includes a plurality of buffer elements. Eachbuffer element contains a unique picture identifier corresponding to onereference picture stored in the frame memory. This means that each ofthe buffer descriptions indicates a plurality of reference picturesstored in the frame memory. The buffer descriptions are also called areference picture set.

Furthermore, the image coding apparatus 100 determines, among thereference pictures indicated in the buffer descriptions, a referencepicture to be assigned as a long-term reference picture.

Here, the long-term reference picture indicates a reference picture thatremains in the frame buffer for a relatively long period of time. Otherthan the long-term reference picture, a normal reference picture thatremains in the frame buffer only for a short period of time is called ashort-term reference picture. This means that the long-term referencepicture is held in the frame buffer for a longer period of time than theshort-term reference picture. In other words, the temporal distance ofthe long-term reference picture from a current picture is longer thanthat of the short-term reference picture (for example, the absolutevalue of a difference in the POC number is large).

In addition, part of the details of the coding and decoding processes isdifferent depending on whether the reference picture to be referred tois the long-term reference picture or the short-term reference picture.For example, the usage of a motion vector in inter prediction isdifferent depending on whether the reference picture to be referred tois the long-term reference picture or the short-term reference picture.

Next, the image coding apparatus 100 writes, into a sequence parameterset (SPS) in the coded bitstream 132, the buffer description defininginformation which defines the determined buffer descriptions (S102).Here, the SPS is a parameter set (header information) in each videosequence. Furthermore, this buffer description defining informationincludes long-term information which identifies, among the referencepictures indicated in the buffer descriptions, a reference picture to beassigned as the long-term reference picture.

Next, the image coding apparatus 100 selects, for each picture, one ofthe buffer descriptions which is to be used to code the picture (S103).It is to be noted that the image coding apparatus 100 may select onebuffer description for each slice.

Next, the image coding apparatus 100 writes buffer description selectinginformation which specifies the selected buffer description into apicture header corresponding to the current picture (or a slice headercorresponding to the current slice) and included in the coded bitstream132 (S104).

Finally, the image coding apparatus 100 codes the current picture orslice using the buffer description selected for the current picture orslice and the long-term information (S105). Furthermore, the imagecoding apparatus 100 generates the coded bitstream 132 which includesthe resulting coded data. It is to be noted that the coding using thelong-term information specifically means executing the coding process(such as an inter prediction process) and managing the frame buffer,assuming the reference picture indicated in the long-term information asthe long-term reference picture.

[Syntax Diagram]

FIGS. 5 and 6 are each a syntax diagram which shows the location of thebuffer description defining information in a coded bitstream in thisembodiment. Two exemplary syntax locations are described in thefollowing.

A coded bitstream 132 shown in FIG. 5 includes SPS 301 (SPS0), aplurality of PPSs 302 (PPS0 and PPS1), and a plurality of picture data303. Each of the picture data 303 includes a picture header 331 and apicture data part 332. The picture data part 332 includes a plurality ofslice data 335.

The SPS 301 includes buffer description defining information 312 (BDdefine) and an SPS identifier 311 (sps_id).

The buffer description defining information 312 defines a plurality ofbuffer descriptions. For example, like the above-mentioned bufferdescriptions 515, the buffer descriptions each include a plurality ofbuffer elements.

Here, the above buffer description defining information 312 includes thefollowing information:

(1) A parameter (NumOfBD or num_short_term_ref_pic_sets) which indicatesthe number of buffer descriptions defined in the SPS;

(2) Para meters (NumOfBE[i], num_negative_pics[i] ornum_negative_pics[i]) which indicate the number of buffer elements ineach buffer description where each index[i] is an index which identifiesa buffer description; and

(3) Parameters (BE[i][j]) which identify a plurality of referencepictures assigned to buffer elements in each buffer description whereeach index[j] is an index which identifies a buffer element, that is,BE[i][j] corresponds to a buffer element identified by the index “j” inthe buffer description identified by the index “i”.

Here, periodic buffer descriptions are defined and created as follows.First, all buffer elements in all buffer descriptions are sequentiallyselected according to a predetermined recursion. Subsequently, theparameters BE[i][j] for assigning a reference picture to each selectedbuffer element are repeatedly created.

Each of the PPSs 302 includes SPS selecting information 321 (sps_select)and a PPS identifier 322 (pps_id). The SPS selecting information 321(e.g. sps_select=0) indicates the SPS 301 which is referred to.Furthermore, each of the PPSs 302 is identified by the unique PPSidentifier 322 (e.g. pps_id=0).

The picture header 331 includes PPS selecting information (pps_select)333 and buffer description selecting information 334 (bd_select).

The PPS selecting information 333 (e.g. pps_select=0) indicates the PPS302 which is referred to. Using this PPS selecting information 333, oneof the PPSs 302 is referred to from the picture header 331. Furthermore,using the SPS selecting information 321 included in the PPS 302, the SPS301 is referred to from the PPS 302 referred to. This links the currentpicture to the available plurality of buffer descriptions defined in theSPS 301.

With the buffer description selecting information 334 (e.g.bd_select=2), one of the buffer descriptions is specified. Thus, onebuffer description is selected out of the plurality of bufferdescriptions.

The slice data 335 included in the picture data 303 is coded and decodedusing ordered reference pictures according to the selected bufferdescription.

Furthermore, as shown in FIG. 6, each of the slice data 335 includes aslice header 341 and a slice data part 342. The slice data part 342includes a plurality of coding unit (CU) data 343.

In a coded bitstream 132A, the PPS selecting information 333 and thebuffer description selecting information 334 are not included in apicture header 331A, but are included in the slice header 341. Also inthis case, the effects the same as those in the case shown in FIG. 5 canbe obtained.

It is to be noted that “slice” in the above explanation may be replacedby “sub-picture unit”. The sub-picture unit includes, for example, atile, an entropy slice, and a group of blocks constituting a wavefrontprocessing sub-picture partition (Wavefront Parallel Processing (WPP)unit).

In this embodiment, for example, in order to assign the long-termreference picture to the buffer element, the picture identifier that isan absolute picture number (such as a POC number) is used. In this case,a reference picture is regarded as a long-term reference picture whenthe reference picture is identified by a picture identifier in thebuffer element. This means that the long-term information included inthe buffer description defining information 312 may include a pictureidentifier which identifies a reference picture to be assigned as thelong-term reference picture.

It is to be noted that a long-term index may be used to assign thelong-term reference picture to the buffer element. In other words, theabove long-term information may include a long-term index whichidentifies the reference picture to be assigned as the long-termreference picture. Specifically, a unique long-term index is firstlyassigned to a reference picture in the frame buffer. Next, the referencepicture is selected using the long-term index assigned to the bufferelement in the buffer description. This means that the long-term indicesare indices which identify a plurality of reference pictures included inthe frame buffer. It is to be noted that the long-term index may be anindex other than the above. For example, the long-term indices may beindices which identify a plurality of long-term reference pictures.

A reference picture is regarded as a long-term reference picture whenthe reference picture is identified by a long-term index in the activebuffer description. It is to be noted that the long-term information mayfurther include information for associating the long-term index with thereference picture which is identified by the picture identifier (POCnumber). This means that the long-term information may further include aunique picture identifier (POC number) for specifying a referencepicture associated with the long-term index. In other words, thelong-term information may include information which indicates acorrespondence relationship between the long-term index and the pictureidentifier (POC number).

When the long-term index having the same value as the value of thelong-term index assigned to the first reference picture is assigned tothe second reference picture which follows the first reference picture,the long-term index specifies the second reference picture and no longerspecifies the first reference picture. For example, the value of thelong-term index assigned to the first reference picture included in thefirst SPS can be directly assigned to the second reference pictureincluded in the second SPS. When the second SPS becomes active, thevalue of the long-term index specifies not the first reference picture,but the second reference picture.

It is to be noted that both the above picture identifier and thelong-term index may be used for assigning a long-term reference pictureto a buffer element. In this case, a reference picture is regarded as along-term reference picture when the reference picture is identified byeither a picture identifier or a long-term index.

It is to be noted that the long-term information may be informationother than the above as long as it assigns a reference picture as along-term reference picture. For example, the long-term information maybe a flag which indicates whether or not the reference picture indicatedby the buffer element is to be assigned as the long-term referencepicture. Alternatively, the long-term information may be informationwhich specifies one or more reference pictures to be assigned aslong-term reference pictures. For this specifying, at least one of theabove-described long-term index and picture identifier (POC number) canbe used, for example. Furthermore, the long-term information may be alist for specifying a plurality of long-term reference pictures.

[Effect of Coding Method]

With the foregoing, the image coding apparatus 100 according to thisembodiment is capable of preventing redundant repetition of the sameparameters for constructing the reference lists in the coded bitstream.This allows the image coding apparatus 100 to improve the codingefficiency of the parameters describing reference list construction.Furthermore, the image coding apparatus 100 is capable of achievingdesign harmonization of the hierarchically structured signaling units ofa coded bitstream.

[Decoding Apparatus]

FIG. 7 is a block diagram which shows a structure of an image decodingapparatus 200 according to this embodiment.

The image decoding apparatus 200 shown in FIG. 7 decodes a codedbitstream 232 on a block-by-block basis, thereby generating decodedimage data 226. This image decoding apparatus 200 includes avariable-length decoding unit 212, an inverse quantization unit 204, aninverse orthogonal transformation unit 205, an adder 206, a block memory207, a frame memory 208, an intra prediction unit 209, an interprediction unit 210, a picture type determination unit 211, and a framememory control unit 213.

The coded bitstream 232 is, for example, the coded bitstream 132generated by the above image coding apparatus 100.

The variable-length decoding unit 212 performs variable-length decoding(entropy decoding) on the coded bitstream 232 to generate quantizedvalues 223 and frame memory control information 233. Here, the framememory control information 233 corresponds to the above frame memorycontrol information 133.

The inverse quantization unit 204 inversely quantizes the quantizedvalues 223, thereby generating frequency coefficients 224. The inverseorthogonal transformation unit 205 performs inverse frequency transformon the frequency coefficients 224, thereby generating prediction errordata 225. The adder 206 adds the prediction error data 225 and theprediction image data 231, thereby generating the decoded image data226. The decoded image data 226 is output from the image decodingapparatus 200 and, for example, is displayed.

The block memory 207 holds the decoded image data 226 as decoded imagedata 227 on a block-by-block basis. The frame memory 208 holds thedecoded image data 226 as decoded image data 228 on a frame-by-framebasis.

The intra prediction unit 209 performs intra prediction to generateprediction image data 229 of a current block to be decoded.Specifically, the intra prediction unit 209 searches within the decodedimage data 227 stored in the block memory 207, and estimates an imagearea which is most similar to the decoded image data 226.

The inter prediction unit 210 performs inter prediction using theper-frame decoded image data 228 stored in the frame memory 208, togenerate prediction image data 230 of the current block.

The picture type determination unit 211 selects one of the predictionimage data 229 and the prediction image data 230 and outputs theselected data as the prediction image data 231.

The frame memory control unit 213 manages the decoded image data 228stored in the frame memory 208. Specifically, the frame memory controlunit 213 performs memory management processes according to the framememory control information 223. The frame memory control unit 213determines whether the decoded image data 128 is kept in the framememory 208 or removed from the frame memory 208. Furthermore, the framememory control unit 213 constructs reference lists to be used by theinter prediction unit 210.

[Decoding Process]

Next, a description is given as to an image decoding method which isperformed by the image decoding apparatus 200 as mentioned above.

FIG. 8 is a flowchart of the image decoding method according to thisembodiment. Furthermore, FIG. 8 shows a decoding process which isperformed on a single video sequence including a plurality of pictures.

Firstly, the image decoding apparatus 200 obtains, from the SPS in thecoded bitstream 232, buffer description defining information whichincludes long-term information and defines a plurality of bufferdescriptions (S201).

Next, the image decoding apparatus 200 obtains buffer descriptionselecting information from a picture header (or a slice header) in thecoded bitstream 232 (S202). For the current picture (or slice), theimage decoding apparatus 200 then selects, out of the bufferdescriptions, one buffer description specified in the buffer descriptionselecting information (S203).

Finally, the image decoding apparatus 200 decodes the current picture(or slice) using the selected buffer description and the long-terminformation (S204). It is to be noted that the decoding using thelong-term information specifically means executing the decoding process(such as an inter prediction process) and managing the frame buffer,assuming the reference picture indicated in the long-term information asthe long-term reference picture.

[Effect of Decoding Method]

With the foregoing, the image decoding apparatus 200 according to thisembodiment is capable of decoding a coded bitstream which is coded inthe form of improved coding efficiency and harmonized design of bufferdescription data.

Embodiment 2

This embodiment describes a variation of the above Embodiment 1. Theimage coding apparatus according to this embodiment further writes, intothe PPS, buffer description updating information for modifying thebuffer descriptions which includes the long-term information.

The following mainly describes differences from Embodiment 1 and thusomits overlapping explanations.

[Coding Apparatus]

The block diagram of the image coding apparatus 100 according to thisembodiment is the same or alike as that shown in FIG. 3 and therefore isnot explained.

[Coding Process]

The following describes an image coding method which is performed by theimage coding apparatus 100 according to this embodiment.

FIG. 9 is a flowchart of an image coding method according to thisembodiment. The processing shown in FIG. 9 additionally includes StepsS301 and S302 as compared to those shown in FIG. 4 in the image codingmethod according to Embodiment 1.

After Step S102, the image coding apparatus 100 modifies a plurality ofbuffer descriptions (S301). Specifically, the image coding apparatus 100modifies one or more buffer descriptions out of the plurality of bufferdescriptions. It is to be noted that the image coding apparatus 100 mayadd new buffer descriptions instead of modifying the original bufferdescriptions. The image coding apparatus 100 may modify some or all ofthe buffer descriptions. For example, the image coding apparatus 100 maymodify some or all of the buffer elements included in the bufferdescriptions. Furthermore, the image coding apparatus 100 determineswhether or not reference pictures included in the modified bufferdescriptions are to be assigned as long-term reference pictures.

Next, for modifying some buffer descriptions out of the plurality ofbuffer descriptions, the image coding apparatus 100 writes, into the PPSin the coded bitstream 132, buffer description updating informationwhich indicates the details of the modification (S302). Here, the bufferdescription updating information includes long-term information forassigning a reference picture as a long-term reference picture.

It is to be noted that, when new buffer descriptions are determined tobe created in Step S301, the buffer description updating informationcomprises information for defining new additional buffer descriptions.

Next, the image coding apparatus 100 selects one buffer description outof the modified plurality of buffer descriptions (S103) and writes, intothe picture header of the current picture in the coded bitstream 132,buffer description selecting information which specifies the selectedbuffer description (S104). Finally, the image coding apparatus 100 codesthe current picture or slice using the selected buffer description andthe long-term information (S105).

[Syntax Diagram]

FIGS. 10 and 11 are each a syntax diagram which shows the location ofthe buffer description updating information in a coded bitstream in thisembodiment. Two exemplary syntax locations are described in thefollowing.

A coded bitstream 132B shown in FIG. 10 is different from the codedbitstream 132 shown in FIG. 5 in that PPS 302B replaces PPS 302.Specifically, the PPS 302B further includes buffer description updatinginformation 323 (BD update).

This buffer description updating information 323 includes: bufferdescription selecting information which specifies a buffer description;buffer element selecting information which specifies a buffer element;and a picture identifier. The picture identifier is included in thebuffer description specified in the buffer description selectinginformation and specifies a picture assigned to the buffer elementspecified in the buffer element selecting information. It is to be notedthat one buffer element corresponds to one reference picture stored inthe frame buffer. It is to be noted that the buffer description updatinginformation 323 may include a plurality of sets of the bufferdescription selecting information, the buffer element selectinginformation, and the picture identifier. In other words, the bufferdescription updating information 323 may include information forupdating a plurality of buffer elements.

Furthermore, when the coded bitstream 132B includes a plurality of PPSs302, the buffer description updating information 323 in one of the PPSs302 is independent of that in another one of the PPSs 302. That is,different PPSs 302 can be associated with different buffer descriptions.For example, when the second PPS is active, the buffer descriptionupdating information 323 included in the first PPS is not used. In thiscase, the buffer description updating information 323 included in theactive second PPS is applied to the buffer description defininginformation 312 included in the SPS 301.

It is to be noted that the same applies to the case where the long-termindex is used. Specifically, when the second PPS is active, thelong-term index included in the active first PPS is not used.

Furthermore, in the buffer description updating information 323, themethod of assigning a long-term reference picture to a buffer elementcan be the same or like as that in the above-described case of thebuffer description defining information 312. In the buffer descriptionupdating information 323, when a reference picture is indicated by thepicture identifier or the long-term index, the reference picture isregarded as a long-term reference picture.

This means that the long-term information included in the bufferdescription updating information 323 may include a picture identifierwhich identifies a reference picture to be assigned as the long-termreference picture. Furthermore, the above long-term information mayinclude a long-term index which identifies the reference picture to beassigned as the long-term reference picture. Moreover, the long-terminformation may further include a unique picture identifier (POC number)for specifying a reference picture associated with the long-term index.

With the foregoing, for the current picture, the PPS 302B indicated inthe PPS selecting information 333 included in the picture header 331 ofthe current picture is referred to, and the buffer description updatinginformation 323 included in the PPS 302B referred to is then referredto. Furthermore, the SPS 301 indicated in the SPS selecting information321 included in the PPS 302B is referred to, and the buffer descriptiondefining information 312 included in the SPS 301 referred to is thenreferred to. When the buffer description updating information 323referred to includes information for updating the buffer descriptionspecified in the buffer description selecting information 334 includedin the above picture header 331, the buffer description updated based onsuch information is used in the process of coding or decoding thecurrent picture. In contrast, when the buffer description updatinginformation 323 referred to does not include the information forupdating the buffer description specified in the buffer descriptionselecting information 334 included in the above picture header 331, thebuffer description which is included in the buffer description defininginformation 312 in the SPS 301 and is specified in the bufferdescription selecting information 334 is used in the process of codingor decoding the current picture.

In a coded bitstream 132C shown in FIG. 11, the PPS selectinginformation 333 and the buffer description selecting information 334 arenot included in the picture header 331A, but are included in the sliceheader 341. Also in this case, the effects the same as those in the caseshown in FIG. 10 can be obtained.

The buffer description updating information 323 may be located insignalling units other than PPS in a coded bitstream. Such othersignalling units possess the same characteristics as the PPS in thatthey contain the parameters used in common by a plurality of slices inone or more pictures. The extension and adaptation from the PPS to theseother signalling units will be apparent to those skilled in the art.

Although the above describes an example in which both the bufferdescription defining information 312 and the buffer description updatinginformation 323 include the long-term information, it may also bepossible that only one of the buffer description defining information312 and the buffer description updating information 323 includes thelong-term information.

[Effect of Coding Method]

With the foregoing, the image coding apparatus 100 according to thisembodiment is capable of preventing redundant repetition of the sameparameters for constructing the reference lists in the coded bitstream.This allows the image coding apparatus 100 to improve the codingefficiency of the parameters describing reference list construction.Furthermore, the image coding apparatus 100 is capable of achievingdesign harmonization of the hierarchically structured signaling units ofa coded bitstream.

[Decoding Apparatus]

The block diagram of the image decoding apparatus 200 according to thisembodiment is the same or alike as that shown in FIG. 7 and therefore isnot explained.

[Decoding Process]

The following describes an image decoding method which is performed bythe image decoding apparatus 200 according to this embodiment.

FIG. 12 is a flowchart of the image decoding method according to thisembodiment. The processing shown in FIG. 12 additionally includes StepS401 as compared to the steps shown in FIG. 8 in the image decodingmethod according to Embodiment 1.

After Step S201, the image decoding apparatus 200 obtains bufferdescription updating information from the PPS in the coded bitstream 232for modifying a plurality of buffer descriptions (S401). Here, thebuffer description updating information includes long-term information.

Next, the image decoding apparatus 200 obtains buffer descriptionselecting information from the picture header of the current picture inthe coded bitstream 232 for selecting one buffer description out of themodified plurality of buffer descriptions (S202). Next, the imagedecoding apparatus 200 selects, for the current picture (or slice), onebuffer description specified in the buffer description selectinginformation (S203). Finally, the image decoding apparatus 200 decodesthe current picture or slice using the selected buffer description andthe long-term information (S204).

[Effect of Decoding Method]

With the foregoing, the image decoding apparatus 200 according to thisembodiment is capable of decoding a coded bitstream which is coded inthe form of improved coding efficiency and harmonized design of bufferdescription data.

Embodiment 3

This embodiment describes a variation of the above Embodiment 2. A codedbitstream in this embodiment is different from that in Embodiment 2 inthe structure of the buffer description updating information. Thefollowing mainly describes differences from Embodiment 1 or 2 and thusomits overlapping explanations.

[Coding Apparatus]

The block diagram of the image coding apparatus 100 according to thisembodiment is the same or alike as that shown in FIG. 3 and therefore isnot explained.

[Coding Process]

The following describes an image coding method which is performed by theimage coding apparatus 100 according to this embodiment.

FIG. 13 is a flowchart of an image coding method according to thisembodiment. The processing shown in FIG. 13 additionally includes StepS301A and S302A as compared to those shown in FIG. 4 in the image codingmethod according to Embodiment 1. Furthermore, the processing in StepS104A is different from that in Step S104.

After Step S103, the image coding apparatus 100 determines modificationsfor the selected buffer description (S301A). Furthermore, the imagecoding apparatus 100 determines whether or not a reference pictureincluded in the modified buffer description is to be assigned as along-term reference picture.

Next, for selecting and modifying the selected buffer description, theimage coding apparatus 100 writes, into the PPS in the coded bitstream132, buffer description updating information which indicates the detailsof the modification (5302A). Here, the buffer description updatinginformation includes long-term information for assigning a referencepicture as a long-term reference picture.

It is to be noted that the structure of the buffer description updatinginformation is almost the same as that in the above Embodiment 2, forexample, but, in this embodiment, the buffer description updatinginformation includes only one set of the buffer description selectinginformation, the buffer element selecting information, and the pictureidentifier.

Next, the image coding apparatus 100 writes PPS selecting informationinto a picture header of a current picture (or a slice header of acurrent slice) in the coded bitstream 132 for indicating that the abovePPS is referred to by the picture (S104A). One corresponding bufferdescription is thereby referred. Finally, the image coding apparatus 100codes the current picture or slice using the selected buffer descriptionand the long-term information (S105).

[Syntax Diagram]

FIGS. 14 and 15 are each a syntax diagram which shows the location ofthe buffer description updating information in a coded bitstream in thisembodiment. Two exemplary syntax locations are described in thefollowing.

A coded bitstream 132D shown in FIG. 14 is different from the codedbitstream 132B shown in FIG. 10 in that buffer description updatinginformation 323D in PPS 302D replaces the buffer description updatinginformation 323 in the PPS 302B. Furthermore, a picture header 331D isdifferent from the picture header 331.

Although the structure of the buffer description updating information323D is almost the same as that of the buffer description updatinginformation 323, for example, the buffer description updatinginformation 323D includes only one set of the buffer descriptionselecting information, the buffer element selecting information, and thepicture identifier.

It is to be noted that the picture header 331D does not include thebuffer description selecting information 334.

With the foregoing, for the current picture, the PPS 302D indicated inthe PPS selecting information 333 included in the picture header 331D ofthe current picture is referred to, and the buffer description updatinginformation 323D included in the PPS 302D referred to is then referredto. Subsequently, the buffer description updating information 323Dreferred to is used in the process of coding or decoding the currentpicture. This means that the pictures or slices which refer to the samePPS 302D are coded and decoded using one updated buffer descriptionindicated in the same buffer description updating information 323D.

In a coded bitstream 132E shown in FIG. 15, the PPS selectinginformation 333 is not included in the picture header 331A, but isincluded in a slice header 341E. Also in this case, the effects the sameas those in the case shown in FIG. 14 can be obtained.

It is to be noted that the buffer description updating information 323Dmay be located in signalling units other than the PPS in a codedbitstream.

[Effect of Coding Method]

With the foregoing, the image coding apparatus 100 according to thisembodiment is capable of preventing redundant repetition of the sameparameters for constructing the reference lists in the coded bitstream.This allows the image coding apparatus 100 to improve the codingefficiency of the parameters describing reference list construction.Furthermore, the image coding apparatus 100 is capable of achievingdesign harmonization of the hierarchically structured signaling units ofa coded bitstream.

[Decoding Apparatus]

The block diagram of the image decoding apparatus 200 according to thisembodiment is the same or alike as that shown in FIG. 7 and therefore isnot explained.

[Decoding Process]

The following describes an image decoding method which is performed bythe image decoding apparatus 200 according to this embodiment.

FIG. 16 is a flowchart of the image decoding method according to thisembodiment. The processing shown in FIG. 16 additionally includes StepS401A as compared to the steps shown in FIG. 8 in the image decodingmethod according to Embodiment 1. Furthermore, the processing in StepsS202A and S203A is different from that in Steps S202 and S203.

After Step S201, the image decoding apparatus 200 obtains, from the PPSin the coded bitstream, buffer description updating informationincluding long-term information and buffer description selectinginformation, for selecting and modifying one buffer description out ofthe plurality of buffer descriptions (S401A).

Next, the image decoding apparatus 200 obtains, from the picture headerof the current picture in the coded bitstream, a PPS identifier forindicating that the above PPS is referred to by the current picture(S202A). Next, the image decoding apparatus 200 selects, for the currentpicture (or slice), one buffer description specified in the bufferdescription selecting information in the PPS specified by the PPSidentifier (S203A). Finally, the image decoding apparatus 200 decodesthe current picture or slice using the selected buffer description andthe long-term information (S204).

[Effect of Decoding Method]

With the foregoing, the image decoding apparatus 200 according to thisembodiment is capable of decoding a coded bitstream which is coded inthe form of improved coding efficiency and harmonized design of bufferdescription data.

Embodiment 4

This embodiment describes a variation of the above Embodiment 3. In thisembodiment, the buffer description updating information is included inthe slice header. The following mainly describes differences fromEmbodiment 1, 2, or 3 and thus omits overlapping explanations.

[Coding Apparatus]

The block diagram of the image decoding apparatus 100 according to thisembodiment is the same or alike as that shown in FIG. 3 and therefore isnot explained.

[Coding Process]

The following describes an image coding method which is performed by theimage coding apparatus 100 according to this embodiment.

FIG. 17 is a flowchart of the image decoding method according to thisembodiment. The processing shown in FIG. 17 includes Step S302B insteadof Steps S302A and S104A shown in FIG. 13 in the image coding methodaccording to Embodiment 3.

After Step S301A, for modifying the selected buffer description, theimage coding apparatus 100 writes, into the slice header of the currentslice in the coded bitstream, buffer description updating informationincluding buffer description selecting information which specifies theselected buffer description (S302B). Here, the buffer descriptionupdating information includes long-term information.

It is to be noted that the structure of the buffer description updatinginformation is the same or alike as that in the above Embodiment 3, forexample.

Finally, the image coding apparatus 100 codes the current slice usingthe selected buffer description and the long-term information (S105).

[Syntax Diagram]

FIG. 18 is a syntax diagram which shows the location of the bufferdescription updating information in a coded bitstream in thisembodiment.

A coded bitstream 132F shown in FIG. 18 is different from the codedbitstream 132E shown in FIG. 15 in that the buffer description updatinginformation 323D is included not in the PPS 302D, but in the sliceheader 341E.

With the foregoing, for the current slice, the buffer descriptionupdating information 323D included in the slice header 341F of thecurrent slice is referred to. Subsequently, the buffer descriptionupdating information 323D referred to is used in the process of codingor decoding the current picture.

Here, the buffer description updating information 323D in one sliceheader 341F is independent of that in another slice header 341F. Inother words, the updating process indicated in the buffer descriptionupdating information 323D included in one slice header 341F is appliedonly to that slice and is not applied to another slice. In addition, thebuffer description updating information 323D included in an active sliceheader 341F is applied to the buffer description defining information312 included in the SPS 301.

The following describes the syntax structure of the SPS 301 and theslice header 341F according to this embodiment. FIG. 19 shows the syntaxstructure of the SPS 301 according to this embodiment. FIG. 20 shows thesyntax structure of the slice header according to this embodiment.

As shown in FIG. 19, the SPS 301 includes the buffer descriptiondefining information 312. The buffer description defining information312 includes long-term information 402 for assigning, as a long-termreference picture, a reference picture indicated by one or more bufferelements included in one or more buffer descriptions. This long-terminformation 402 includes a picture identifier 403 (such as a POC number)and a long-term index 404.

As shown in FIG. 20, the slice header 341F (or sub-picture unit)includes the buffer description updating information 323D. The bufferdescription updating information 323D is information for selecting oneof the buffer descriptions and updating the selected buffer description.This buffer description updating information 323D includes the bufferdescription selecting information 334 and long-term information 405 forassigning, as a long-term reference picture, a reference pictureindicated by one or more buffer elements included in one or more bufferdescriptions. This long-term information 405 includes a long-term index406 and a picture identifier 407 (POC number).

It is to be noted that either only one or both of the picture identifier407 and the long-term index 406 which are included in the slice header341F may be used for assigning a long-term reference picture to a bufferelement. Likewise, either only one or both of the picture identifier 403and the long-term index 404 which are included in the SPS 301 may beused for assigning a long-term reference picture to a buffer element.

It is to be noted that the same or like syntax structure may be usedalso in the other embodiments described above. For example, also in theabove Embodiment 1, the syntax structure of SPS shown in FIG. 19 may beused. Furthermore, in Embodiment 1, the slice header 341 includes thebuffer description selecting information 334(short_term_ref_pic_set_idx).

[Effect of Coding Method]

With the foregoing, the image coding apparatus 100 according to thisembodiment is capable of preventing redundant repetition of the sameparameters for constructing the reference lists in the coded bitstream.This allows the image coding apparatus 100 to improve the codingefficiency of the parameters describing reference list construction.Furthermore, the image coding apparatus 100 is capable of achievingdesign harmonization of the hierarchically structured signaling units ofa coded bitstream.

[Decoding Apparatus]

The block diagram of the image decoding apparatus 200 according to thisembodiment is the same or alike as that shown in FIG. 7 and therefore isnot explained.

[Decoding Process]

The following describes an image decoding method which is performed bythe image decoding apparatus 200 according to this embodiment.

FIG. 21 is a flowchart of the image decoding method according to thisembodiment. The processing shown in FIG. 21 includes Step S401B insteadof Step S202 shown in FIG. 8 in the image decoding method according toEmbodiment 1.

After Step S201, the image decoding apparatus 200 obtains, from theslice header of the current slice in the coded bitstream, bufferdescription updating information including buffer description selectinginformation, for selecting and modifying one buffer description out ofthe plurality of buffer descriptions (S401B). Here, the bufferdescription updating information includes long-term information.

Next, the image decoding apparatus 200 selects the buffer descriptionspecified in the buffer description selecting information (S203).Finally, the image decoding apparatus 200 decodes the current sliceusing the selected buffer description and the long-term information(S204).

[Effect of Decoding Method]

With the foregoing, the image decoding apparatus 200 according to thisembodiment is capable of decoding a coded bitstream which is coded inthe form of improved coding efficiency and harmonized design of bufferdescription data.

As above, in the image coding method according to this embodiment, thebuffer description defining information which defines a plurality ofbuffer descriptions is written into the SPS corresponding to the codedbitstream.

Furthermore, in the image coding method, for each processing unit thatis a picture or a slice, one of the buffer descriptions is selected, andbuffer description selecting information which specifies the selectedbuffer description is written into a first header of the processing unitwhich is included in the coded bitstream. Here, the first header is aheader of a picture or a slice and specifically is PPS, a pictureheader, or a slice header.

In the image coding method, the processing unit is coded using theselected buffer description.

Furthermore, the above buffer description defining information includeslong-term information for assigning a reference picture as a long-termreference picture.

As above, in the image coding method, the buffer description defininginformation including the long-term information is written into thesequence parameter set shared by a plurality of pictures, and a bufferdescription identifier indicating a buffer description to be selected iswritten into a header of each picture or slice. This allows a reductionin redundant information and thereby allows an improvement in codingefficiency in the image coding method as compared to the case where thebuffer description defining information is written into a pictureparameter set. Furthermore, in the image coding method, it is possibleto reduce redundant information and therefore possible to improve thecoding efficiency as compared to the case where the long-terminformation is written into a slice header.

Although the image coding apparatus and the image decoding apparatusaccording to the embodiments of the present disclosure have beendescribed above, the present disclosure is not limited theseembodiments.

For example, although the above describes an example in which the SPS isincluded in the coded bitstream which includes slice data and the like,the SPS may be transmitted from the image coding apparatus to the imagedecoding apparatus separately from the coded bitstream which includesthe slice data and the like.

Respective processing units included in the image coding apparatus andthe image decoding apparatus according to each of the above embodimentsare typically implemented as a large scale integration (LSI) that is anintegrated circuit. These processing units may be each provided on asingle chip, and part or all of them may be formed into a single chip.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor can also achieve theintegration. Field Programmable Gate Array (FPGA) that can be programmedafter manufacturing LSIs, or a reconfigurable processor that allowsre-configuration of the connection or configuration of an LSI can beused for the same purpose.

Each of the structural elements in each of the above-describedembodiments may be configured in the form of an exclusive hardwareproduct, or may be realized by executing a software program suitable forthe structural element. Each of the structural elements may be realizedby means of a program executing unit, such as a CPU and a processor,reading and executing the software program recorded on a recordingmedium such as a hard disk or a semiconductor memory.

Furthermore, the present disclosure may be implemented as the abovesoftware program and may also be implemented as a non-transitorycomputer-readable recording medium on which such a program is recorded.In addition, it goes without saying that such a program may bedistributed via a communication network such as the Internet.

The numerals herein are all given to specifically illustrate the presentdisclosure and therefore do not limit it.

The segmentation of the functional blocks in each block diagram is anexample, and some of the functional blocks may be implemented as onefunctional block while one functional block may be divided into pluralparts, or part of the function of one functional block may be shifted toanother functional block. Furthermore, the functions of a plurality offunctional blocks which have similar functions may be processed inparallel or in time-sliced fashion by single hardware or software.

The processing order of the steps included in the above image coding ordecoding method is given to specifically illustrate the inventiveconcept and therefore may be any other order. Part of the above stepsmay be performed at the same time as (in parallel with) another step.

Embodiment 5

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method and the moving picture decoding methoddescribed in each of embodiments. The recording media may be anyrecording media as long as the program can be recorded, such as amagnetic disk, an optical disk, a magnetic optical disk, an IC card, anda semiconductor memory.

Hereinafter, the applications to the moving picture coding method andthe moving picture decoding method described in each of embodiments andsystems using thereof will be described. The system has a feature ofhaving an image coding and decoding apparatus that includes an imagecoding apparatus using the image coding method and an image decodingapparatus using the image decoding method. Other configurations in thesystem can be changed as appropriate depending on the cases.

FIG. 22 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 22, and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long-term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent disclosure), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 23. More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent disclosure). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (ii) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 24 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present disclosure); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 25 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 26 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 24. Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 27A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 27B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments, and transmitsthe coded video data to the multiplexing/demultiplexing unit ex353. Incontrast, during when the camera unit ex365 captures video, stillimages, and others, the audio signal processing unit ex354 codes audiosignals collected by the audio input unit ex356, and transmits the codedaudio data to the multiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present disclosure),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably has 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, the inventive concept is not limited to each ofembodiments, and various modifications and revisions can be made in anyof the embodiments in the present disclosure.

Embodiment 6

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconforms cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 28 illustrates a structure of the multiplexed data. As illustratedin FIG. 28, the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 29 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 30 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 30 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 30, the video stream is divided into pictures as I-pictures,B-pictures, and P-pictures each of which is a video presentation unit,and the pictures are stored in a payload of each of the PES packets.Each of the PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 31 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 31. The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 32 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 33. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 33, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 34, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 35 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 7

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 36 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present disclosureis applied to biotechnology.

Embodiment 8

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 37illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 36.Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 36. TheCPU ex502 determines to which standard the video data conforms. Then,the driving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on the signal from the CPUex502. For example, the identification information described inEmbodiment 8 is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment 8 but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 39. The driving frequency can be selected by storing the look-uptable in the buffer ex508 and in an internal memory of an LSI, and withreference to the look-up table by the CPU ex502.

FIG. 38 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiments.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 9

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 40A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present disclosure. Since the aspect of thepresent disclosure is characterized by frame memory control inparticular, for example, the dedicated decoding processing unit ex901 isused for frame memory control. Otherwise, the decoding processing unitis probably shared for one of the entropy decoding, deblockingfiltering, and motion compensation, or all of the processing. Thedecoding processing unit for implementing the moving picture decodingmethod described in each of embodiments may be shared for the processingto be shared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 40B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present disclosure, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present disclosure and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentdisclosure and the processing of the conventional standard,respectively, and may be the ones capable of implementing generalprocessing. Furthermore, the configuration of the present embodiment canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present disclosure and the moving picturedecoding method in conformity with the conventional standard.

Although the image coding apparatus and the image decoding apparatusaccording to one or more aspects of the inventive concepts have beendescribed above, the herein disclosed subject matter is to be considereddescriptive and illustrative only. Those skilled in the art will readilyappreciate that the appended Claims are of a scope intended to cover andencompass not only the particular embodiments disclosed, but alsoequivalent structures, methods, and/or uses which are obtained by makingvarious modifications in the embodiments and by arbitrarily combiningthe structural elements in different embodiments, without materiallydeparting from the principles and spirit of the inventive concept.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to image coding methods, imagedecoding methods, image coding apparatuses, and image decodingapparatuses. The present disclosure can be used for information displaydevices and imaging devices with high resolution which includetelevisions, digital video recorders, car navigation systems, cellularphones, digital cameras, and digital video cameras.

The invention claimed is:
 1. An image coding method for coding picturesinto a coded bitstream, the image coding method comprising: writing,into a sequence header, buffer descriptions that specify referencepictures to be held in a buffer for coding the pictures, the bufferdescriptions including long-term information which identifies areference picture, among a plurality of reference pictures covered bythe buffer descriptions, to be assigned as a long-term referencepicture; selecting one of the buffer descriptions for a slice in one ofthe pictures; writing, into a header of the slice, selecting informationfor specifying the selected buffer description; and coding the sliceusing the reference picture to be assigned as the long-term referencepicture identified by the selected buffer description, wherein syntaxelements included in the sequence header and including the bufferdescriptions are applied to all of the pictures in the coded bitstream,wherein syntax elements included in the header of the slice andincluding the selecting information are applied to all blocks in theslice, wherein the long-term information, which is written into thesequence header, includes (i) a long-term index for identifying thereference picture to be assigned as the long-term reference picture and(ii) a unique picture order count (POC) number for specifying thereference picture identified by the long-term index.
 2. An image codingapparatus for coding pictures into a coded bitstream, the image codingapparatus comprising: a processor; and a non-transitory memory havingstored thereon executable instructions, which when executed by theprocessor, cause the processor to perform the following: writing, into asequence header, buffer descriptions that specify reference pictures tobe held in a buffer for coding the pictures, the buffer descriptionsincluding long-term information which identifies a reference picture,among a plurality of reference pictures covered by the bufferdescriptions, to be assigned as a long-term reference picture; selectingone of the buffer descriptions for a slice in one of the pictures;writing, into a header of the slice, selecting information forspecifying the selected buffer description; and coding the slice usingthe reference picture to be assigned as the long-term reference pictureidentified by the selected buffer description, wherein syntax elementsincluded in the sequence header and including the buffer descriptionsare applied to all of the pictures in the coded bitstream, whereinsyntax elements included in the header of the slice and including theselecting information are applied to all blocks in the slice, whereinthe long-term information, which is written into the sequence header,includes (i) a long-term index for identifying the reference picture tobe assigned as the long-term reference picture and (ii) a unique pictureorder count (POC) number for specifying the reference picture identifiedby the long-term index.